1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
As magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced. Here, the length of the track width defining portion orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the above-mentioned medium facing surface. This medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the Published U.S. Patent Application No. 2003/0151850A1, the Published Unexamined Japanese Patent Application 2003-203311, and the U.S. Pat. No. 6,504,675B1, for example. According to this technique, the end of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located on the air-inflow-end side of the slider) is smaller than the other side. Typically, in the medium facing surface of a magnetic head, the end farther from the substrate is located forward in the direction of travel of the recording medium (that is, the side located on the air-outflow-end side of the slider). Therefore, the shape of the end of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is smaller than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a pole layer and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end of the shield is located forward of an end of the pole layer along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
The U.S. Pat. No. 4,672,493 discloses a magnetic head having a structure in which magnetic layers are provided forward and backward, respectively, in the direction of travel of the recording medium with respect to a middle magnetic layer to be the pole layer, and coils are disposed between the middle magnetic layer and the forward magnetic layer, and between the middle magnetic layer and the backward magnetic layer, respectively. This magnetic head is capable of increasing components orthogonal to the surface of the recording medium among components of the magnetic field generated from the medium-facing-surface-side end of the middle magnetic layer.
Consideration will now be given to a method of forming a pole layer whose end located in the medium facing surface has a shape in which the side closer to the substrate is smaller than the side farther from the substrate, as mentioned above. In prior art, frame plating has been often employed as a method of forming such a pole layer. According to the method of forming the pole layer by frame plating, an electrode film is first formed on a base layer for the pole layer. Next, a photoresist layer is formed on the electrode film. The photoresist layer is then patterned to form a frame having a groove whose shape corresponds to the pole layer. Next, plating is performed by feeding a current to the electrode film to form the pole layer in the groove. The frame is then removed. Next, portions of the electrode film except the portion below the pole layer are removed. This method of forming the pole layer by frame plating has the following problem.
As the track width is reduced, the length of the side of the end of the track width defining portion closer to the substrate becomes closer to zero. As a result, it is impossible to grow the plating layer to be the track width defining portion on the electrode film. Therefore, the problem is that it is difficult to reduce the track width when the pole layer is formed by frame plating.
To solve this problem, it is possible that, after forming the pole layer by frame plating, both side portions of the track width defining portion are etched by dry etching such as ion beam etching so as to reduce the track width. According to this method, however, the length of the side of the end of the track width defining portion closer to the substrate becomes closer to zero as the track width is reduced, and the track width defining portion may be thereby broken down. It is thus difficult to reduce the track width by this method, too.
To form the pole layer by frame plating, it is required to remove portions of the electrode film except the portion below the pole layer after the pole layer is formed. This removal of the electrode film is performed by dry etching such as ion beam etching. When this removal is performed, both side portions of the pole layer are etched, too. As a result, the neck height becomes greater than a desired height, or the pole layer goes out of a desired shape. Also in the case where the pole layer is formed by frame plating and then both side portions of the track width defining portion are etched to reduce the track width as described above, the neck height becomes greater than a desired height, or the pole layer goes out of a desired shape. If the neck height is greater than a desired height, or if the pole layer goes out of a desired shape as mentioned above, the overwrite property is reduced.
When frame plating is employed to form the pole layer, the pole layer is polished, after it is formed, by chemical mechanical polishing (hereinafter referred to as CMP), for example, to flatten the top surface of the pole layer and to make the pole layer have a desired thickness. Here, both side portions of the track width defining portion are tilted with respect to the direction orthogonal to the substrate surface. Therefore, if the point at which polishing of the pole layer is stopped varies, the track width varies. For example, it is assumed that an angle of 7 degrees is formed between the direction orthogonal to the substrate surface and each of the side portions of the track width defining portion. In this case, if the point at which polishing of the pole layer is stopped is shifted by 0.05 μm, the track width varies by 0.0123 μm. As another example, it is assumed that an angle of 10 degrees is formed between the direction orthogonal to the substrate surface and each of the side portions of the track width defining portion. In this case, if the point at which polishing of the pole layer is stopped is shifted by 0.05 μm, the track width varies by 0.0176 μm.
The Published U.S. Patent Application No. 2003/0151850A1 discloses a method in which a groove having a shape corresponding to the pole layer is formed in an inorganic insulating film, and the pole layer is formed in the groove by plating or sputtering. In this method the width of the pole layer, that is, the track width, is defined by the width of the groove formed in the inorganic insulating film. Therefore, it is required to reduce the width of the groove to reduce the track width. However, this method has a problem that it is difficult to form a groove having a shape corresponding to the pole layer and having a small width in the inorganic insulating film.